package com.xiannimei.util;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.OutputStream;

/**
 * Base64Util 避免保留字冲突的自定义base64编码器
 * 
 * 2013-7-9 下午3:40:40
 * 
 * @author xinyuan.guo
 * 
 */
public class Base64Util {
	protected final static byte[] encodingTable = { (byte) 'A', (byte) 'B', (byte) 'C', (byte) 'D', (byte) 'E',
			(byte) 'F', (byte) 'G', (byte) 'H', (byte) 'I', (byte) 'J', (byte) 'K', (byte) 'L', (byte) 'M', (byte) 'N',
			(byte) 'O', (byte) 'P', (byte) 'Q', (byte) 'R', (byte) 'S', (byte) 'T', (byte) 'U', (byte) 'V', (byte) 'W',
			(byte) 'X', (byte) 'Y', (byte) 'Z', (byte) 'a', (byte) 'b', (byte) 'c', (byte) 'd', (byte) 'e', (byte) 'f',
			(byte) 'g', (byte) 'h', (byte) 'i', (byte) 'j', (byte) 'k', (byte) 'l', (byte) 'm', (byte) 'n', (byte) 'o',
			(byte) 'p', (byte) 'q', (byte) 'r', (byte) 's', (byte) 't', (byte) 'u', (byte) 'v', (byte) 'w', (byte) 'x',
			(byte) 'y', (byte) 'z', (byte) '0', (byte) '1', (byte) '2', (byte) '3', (byte) '4', (byte) '5', (byte) '6',
			(byte) '7', (byte) '8', (byte) '9', (byte) '-', (byte) '_' };

	protected static byte padding = (byte) '.';

	/**
	 * set up the decoding table.
	 */
	protected final static byte[] decodingTable = new byte[128];
	
	static {
		for (int i = 0; i < encodingTable.length; i++) {
			decodingTable[encodingTable[i]] = (byte) i;
		}
	}

	/***
	 * encode the input data producing a base 64 encoded byte array.
	 * 
	 * @return a byte array containing the base 64 encoded data.
	 */
	public static String encode(byte[] data) {
		ByteArrayOutputStream bOut = new ByteArrayOutputStream();

		try {
			encode(data, 0, data.length, bOut);
		} catch (IOException e) {
			throw new RuntimeException("exception encoding base64 string: " + e);
		}

		return new String(bOut.toByteArray());
	}

	/***
	 * encode the input data producing a base 64 output stream.
	 * 
	 * @return the number of bytes produced.
	 */
	public static int encode(byte[] data, int off, int length, OutputStream out) throws IOException {
		int modulus = length % 3;
		int dataLength = (length - modulus);
		int a1, a2, a3;

		for (int i = off; i < off + dataLength; i += 3) {
			a1 = data[i] & 0xff;
			a2 = data[i + 1] & 0xff;
			a3 = data[i + 2] & 0xff;

			out.write(encodingTable[(a1 >>> 2) & 0x3f]);
			out.write(encodingTable[((a1 << 4) | (a2 >>> 4)) & 0x3f]);
			out.write(encodingTable[((a2 << 2) | (a3 >>> 6)) & 0x3f]);
			out.write(encodingTable[a3 & 0x3f]);
		}

		/**
		 * process the tail end.
		 */
		int b1, b2, b3;
		int d1, d2;

		switch (modulus) {
			case 0 :
				/** nothing left to do */
				break;
			case 1 :
				d1 = data[off + dataLength] & 0xff;
				b1 = (d1 >>> 2) & 0x3f;
				b2 = (d1 << 4) & 0x3f;

				out.write(encodingTable[b1]);
				out.write(encodingTable[b2]);
				out.write(padding);
				out.write(padding);
				break;
			case 2 :
				d1 = data[off + dataLength] & 0xff;
				d2 = data[off + dataLength + 1] & 0xff;

				b1 = (d1 >>> 2) & 0x3f;
				b2 = ((d1 << 4) | (d2 >>> 4)) & 0x3f;
				b3 = (d2 << 2) & 0x3f;

				out.write(encodingTable[b1]);
				out.write(encodingTable[b2]);
				out.write(encodingTable[b3]);
				out.write(padding);
				break;
		}

		return (dataLength / 3) * 4 + ((modulus == 0) ? 0 : 4);
	}

	private static boolean ignore(char c) {
		return (c == '\n' || c == '\r' || c == '\t' || c == ' ');
	}

	/***
	 * decode the base 64 encoded String data - whitespace will be ignored.
	 * 
	 * @return a byte array representing the decoded data.
	 */
	public static byte[] decode(String data) {
		ByteArrayOutputStream bOut = new ByteArrayOutputStream();

		try {
			decode(data, bOut);
		} catch (IOException e) {
			throw new RuntimeException("exception decoding base64 string: " + e);
		}

		return bOut.toByteArray();
	}

	/***
	 * decode the base 64 encoded String data writing it to the given output
	 * stream, whitespace characters will be ignored.
	 * 
	 * @return the number of bytes produced.
	 */
	public static int decode(String data, OutputStream out) throws IOException {
		byte b1, b2, b3, b4;
		int length = 0;

		int end = data.length();

		while (end > 0) {
			if (!ignore(data.charAt(end - 1))) {
				break;
			}

			end--;
		}

		int i = 0;
		int finish = end - 4;

		i = nextI(data, i, finish);

		while (i < finish) {
			b1 = decodingTable[data.charAt(i++)];

			i = nextI(data, i, finish);

			b2 = decodingTable[data.charAt(i++)];

			i = nextI(data, i, finish);

			b3 = decodingTable[data.charAt(i++)];

			i = nextI(data, i, finish);

			b4 = decodingTable[data.charAt(i++)];

			out.write((b1 << 2) | (b2 >> 4));
			out.write((b2 << 4) | (b3 >> 2));
			out.write((b3 << 6) | b4);

			length += 3;

			i = nextI(data, i, finish);
		}

		length += decodeLastBlock(out, data.charAt(end - 4), data.charAt(end - 3), data.charAt(end - 2),
				data.charAt(end - 1));

		return length;
	}

	private static int decodeLastBlock(OutputStream out, char c1, char c2, char c3, char c4) throws IOException {
		byte b1, b2, b3, b4;

		if (c3 == padding) {
			b1 = decodingTable[c1];
			b2 = decodingTable[c2];

			out.write((b1 << 2) | (b2 >> 4));

			return 1;
		} else if (c4 == padding) {
			b1 = decodingTable[c1];
			b2 = decodingTable[c2];
			b3 = decodingTable[c3];

			out.write((b1 << 2) | (b2 >> 4));
			out.write((b2 << 4) | (b3 >> 2));

			return 2;
		} else {
			b1 = decodingTable[c1];
			b2 = decodingTable[c2];
			b3 = decodingTable[c3];
			b4 = decodingTable[c4];

			out.write((b1 << 2) | (b2 >> 4));
			out.write((b2 << 4) | (b3 >> 2));
			out.write((b3 << 6) | b4);

			return 3;
		}
	}

	private static int nextI(String data, int i, int finish) {
		while ((i < finish) && ignore(data.charAt(i))) {
			i++;
		}
		return i;
	}
}
